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What is meant by heuristic optimisation? Discuss the main heuristics that are applied during query optimisation.
Ans: In heuristic optimization, heuristics are employed to reduce the cost of optimization in place of analyzing the number of different plans to make out the optimal plan. For instance, a heuristic optimizer would make use of the rule 'Perform selection operation as early as possible' without finding out whether the cost is reduced by this transformation. Heuristics approach generally assists to reduce the cost but not all the time. The major heuristics that are applied throughout query optimization are:
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Suppose an instruction takes 1 nanosecond to execute (on average), a page fault takes 20 microseconds of processor time, and it takes 300 microseconds of disk time to read or write
Explain in details about Data Sharing
How can you map NULL values to other values while display? IF( ) , IFNULL( ) keywords are used to do so. They are 'LIMIT' is used for the following kinds of problems: 1) Ans
why data in an RDMS need to be normalised
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Which element in the database can modified by changing the data dictionary? Data elements in the database can be changed or modified through changing the data dictionary.
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